After the discovery of carbon nanotubes by Iijima (Nature, 354, p.56, 1991), nanotubes and nanowires/nanorods of various materials, including Si, SiC, Ge, etc, have been synthesized (Zhang et al., Applied Physics Letter, 72, p.1835, 1998; Dai et al., Nature, 375, p. 769, 1995).
For potential mechanical applications, silicon carbide nanorods have attracted great interest because micrometer-sized SiC whiskers are widely used to strengthen composite materials. Recent work reported that the elasticity and strength of SiC nanostructures are considerably greater than those of larger SiC structures. The physical and electrical properties of silicon carbide also make it an interesting semiconductor for high temperature, high power and high speed device applications.
Various growth techniques have been used to synthesize SiC whiskers with diameters in micrometer or sub-micrometer scale, for example, carbothermal reduction of silica (Hollar and Kim, Ceramic Engineering Science Proceeding, 12, p. 979, 1991), decomposition of organic silicon compounds (Addamiano, Journal of Crystal Growth, 58, p.617, 1982) and reduction between silicon halides and tetrachloromethane (Janeuay, Ceramic Industry, 4, p.42, 1992), etc. Dai et al. (Nature (London), 375, p.769, 1995) have reported the synthesis of SiC nanorods by a two-step method, called carbon nanotube template-mediated growth. However, this process requires the preparation of carbon nanotubes before obtaining SiC nanorods, which implies additional production steps and increased cost. Recently, beta-SiC nanorods with diameters of about 30 nm have been prepared by carbothermal reduction of sol-gel derived silica xerogels containing carbon nano-particles (Meng et al., Solid State Communications, 106, p.215, 1998). However, as the nanorods have to be grown on the surface of xerogels, this method can hardly be applied for electronic device fabrication.
Carbon nanotubes are one of the popular materials used in field-emitters (W. A. de Heer et al., Science, 270, p. 1179, 1995), but silicon carbide nanorods have never been used in this field.
For the purpose of the present specification the term "nanorod" should be understood to define a filament having a diameter of the order of 10 to 100 nm.